The present invention relates to a pump transmission particularly suited for a small boat including a water jet propeller.
FIG. 1 schematically shows a small boat of the type to which this invention is applicable. The boat includes a hull 28, made, for example, of fiber reinforced plastic, which houses a fuel tank 29 and an engine 1 including a crankshaft 2. The engine 1 drives a water jet propeller 5 which is coupled to the shaft 2 and is supported within a duct 30 formed in the hull adjacent the stern. The propeller 5 includes an impeller shaft 8 supported by an impeller bearing 6 mounted within the duct. The boat has a pump transmission which includes an intermediate shaft 11 interconnecting the crankshaft 2 and the impeller shaft 8 through fore and aft couplings 10 and 10a. The intermediate shaft 11 is supported by an intermediate bearing unit 16 mounted on a bulkhead 3 of the hull 28.
FIG. 2 shows in detail a part of a conventional pump transmission used in a boat of the character shown in FIG. 1. In FIG. 2, the forward coupling 10 mounted on the crankshaft 2 of the engine 1 is coupled to the intermediate shaft 11 through an outer sleeve 10b and axial splines 12. A similar coupling arrangement is also used at an aft coupling 10a. The intermediate shaft 11 is journaled by the intermediate bearing unit 16, which includes a bearing case having an integrally formed sleeve 22 and flange 24 fixed to a bulkhead 3. An inner sleeve 18 and bearings 37 are mounted between the bearing case and the shaft 11.
The intermediate shaft 11 is supported in a fixed position and at a fixed angle by the bulkhead 3. The crankshaft 2 and the impeller shaft 8 are coupled in angularly fixed relation to the intermediate shaft 11. However, since the engine 1 is usually mounted on resilient cushions, the crankshaft 2 is likely to become offset from the axis of the intermediate shaft 11 during operation. However, such an offset is not accommodated or absorbed by this fixed arrangement of the shafts. Also, in the conventional arrangement, since the water jet propeller shown in FIG. 1 is mounted on the hull, the impeller shaft 8 may become offset from the intermediate shaft 11 during operation. However, such an offset is not accommodated because the intermediate shaft 11 is supported in fixed relation to the bearing unit 16.
In order to remedy this situation, laborious shimming adjustments have been necessary when the engine 1 (or the impeller bearing) is mounted.
Furthermore, the fixed arrangement of the intermediate shaft 11 on the bearing unit 16 produces large loads on the connection between the crankshaft 2 and the shaft 11, on the bearing unit 16, and in turn on the bulkhead 3. This may lower the durability of the parts.